JP5029921B2 - Method for manufacturing solar battery cell - Google Patents

Description

The present invention relates to a method for manufacturing a solar battery cell, and more particularly to a method for manufacturing a solar battery cell that can effectively suppress a decrease in output even when the area of the back surface increases.

In recent years, development of clean energy has been demanded due to problems of depletion of energy resources and global environmental problems such as an increase in CO _{2 in} the atmosphere. In particular, solar power generation using solar cells is a new energy source. It has been developed, put into practical use, and is on the path of development.

  Conventionally, for example, a solar cell diffuses an impurity having a conductivity type opposite to that of a silicon substrate into a surface (light-receiving surface) on a side where sunlight enters, out of a surface of a monocrystalline or polycrystalline silicon substrate. Thus, a pn junction is formed, and electrodes are formed on the light receiving surface of the silicon substrate and the back surface on the opposite side. It is also common to increase the output by the back surface field effect by diffusing impurities of the same conductivity type as the silicon substrate at a high concentration on the back surface of the silicon substrate.

  However, in the solar cell having such a structure, there is a problem that the output of the solar cell is lowered because the electrode formed on the light receiving surface blocks sunlight incident thereon. Therefore, so-called back junction solar cells have been developed in which electrodes are not formed on the light receiving surface of a silicon substrate, but electrodes of different conductivity types are formed only on the back surface of the silicon substrate.

  In a back junction solar cell, power can be extracted only from the back side of the silicon substrate on which the electrode is formed. Therefore, the structure of the electrode is very important from the viewpoint of the output of the back junction solar cell. is there.

  FIG. 13 shows a schematic cross-sectional view of an example of a conventional back junction solar cell. In this conventional back junction solar cell, for example, an antireflection film 109 is formed on the light receiving surface of a p-type silicon substrate 101, and an n + layer 105 and a p + layer 106 are formed on the back surface of the silicon substrate 101. Are formed at predetermined intervals alternately. A finger p electrode 111 is formed on the p + layer 106, and a finger n electrode 112 is formed on the n + layer 105.

  When sunlight is incident on the light receiving surface of the back junction solar cell, carriers generated in the vicinity of the light receiving surface of the semiconductor substrate 101 reach the pn junction formed on the back surface, and reach the finger p electrode 111 and the finger n electrode 112. Collected and taken out.

  FIG. 14 shows a schematic plan view of an example of an electrode structure on the back surface of a conventional back junction solar cell. In this conventional electrode structure, from the viewpoint of improving the output of the solar battery cell, the finger p electrode 111 and the finger n electrode 112 are formed inside the back surface of the silicon substrate 101 so as to cover the entire back surface. A bus bar p-electrode 113 that intersects the finger p-electrode 111 and a bus-bar n-electrode 114 that intersects the finger n-electrode 112 are formed at the end of the back surface of 101.

Here, since the finger p electrode 111 and the finger n electrode 112 lose output when the series resistance is increased, the sectional area (electrode width × height) is generally increased from the viewpoint of reducing the series resistance. Designed as such. However, when the area of the back surface of the solar battery cell is increased, the length L ₀ of the finger p-electrode 111 and the finger n-electrode 112 needs to be longer, but the height of these electrodes is limited, In order to increase the cross-sectional area, it was necessary to increase the electrode width W ₀ . When the electrode width W ₀ is increased, the pitch P ₀ between the finger p electrode 111 and the finger n electrode 112 is increased, and the carrier moving distance in the silicon substrate 101 is increased, and the output of the solar cell is increased. There was a problem that would decrease.

JP 2002-359388 A JP 2001-68699 A

The objective of this invention is providing the manufacturing method of the photovoltaic cell which can suppress effectively the fall of an output, even when the area of a back surface becomes large.

The present invention relates to a method of manufacturing a solar cell in which a p + layer and an n + layer are formed on the back surface opposite to the light receiving surface of a semiconductor substrate, and the p-type impurity containing p-type impurities on the back surface of the semiconductor substrate. A step of attaching a paste material and an n-type paste material containing an n-type impurity, a step of forming a diffusion prevention film on the back surface of the semiconductor substrate so as to cover the p-type paste material and the n-type paste material , and heating the semiconductor substrate A step of diffusing the p-type impurity contained in the p-type paste material into the semiconductor substrate to form a p + layer, and the semiconductor substrate is heated to diffuse the n-type impurity contained in the n-type paste material into the semiconductor substrate. And a step of forming an n + layer, and in the step of forming the texture structure, the diffusion prevention film is a method for manufacturing a solar cell that also serves as an etching mask when forming the texture structure .

Further, in the method for manufacturing a solar cell of the present invention, the diffusion preventing film is preferably Rukoto such a silicon oxide film.

ADVANTAGE OF THE INVENTION According to this invention, even when the area of a back surface becomes large , the manufacturing method of the photovoltaic cell which can suppress effectively the fall of an output can be provided.

It is typical sectional drawing after the slice from the ingot of the silicon substrate used for this invention. It is typical sectional drawing after the etching of the damage layer of the silicon substrate used for this invention. It is typical sectional drawing after formation of the diffusion prevention film of the silicon substrate used for this invention. It is typical sectional drawing after formation of the p <+> layer and n <+> layer of the silicon substrate used for this invention. It is typical sectional drawing after formation of the texture structure of the silicon substrate used for this invention. It is typical sectional drawing after the removal of the diffusion protective film and paste material of a silicon substrate used for this invention. It is typical sectional drawing after formation of the passivation film of the silicon substrate used for this invention. It is typical sectional drawing after the removal of the passivation film of the silicon substrate used for this invention. It is typical sectional drawing after electrode formation of the silicon substrate used for this invention. It is a typical top view of a preferable example of the electrode structure of the back surface of the photovoltaic cell of this invention. It is a schematic plan view of another preferred example of the electrode structure on the back surface of the solar battery cell of the present invention. It is a typical top view of a preferable example of the electrode structure of the back surface of the solar cell module of this invention. It is typical sectional drawing of an example of the conventional back junction type photovoltaic cell. It is a typical top view of an example of the electrode structure of the back surface of the conventional back junction type photovoltaic cell.

  Embodiments of the present invention will be described below. In the drawings of the present application, the same reference numerals represent the same or corresponding parts.

  The schematic cross-sectional views of FIGS. 1 to 9 show a preferred example of the manufacturing process of the solar battery cell of the present invention. First, as shown in FIG. 1, a silicon substrate 1 as a semiconductor substrate obtained by slicing an ingot of a silicon crystal has a damaged layer 1a in the vicinity of the surface at the time of slicing. Therefore, as shown in FIG. 2, the damaged layer 1a is etched using an acidic or alkaline solution. Here, the silicon substrate 1 may be n-type or p-type, and the size and thickness of the silicon substrate 1 are not limited. However, when a pyramidal microstructure called a texture is formed on the light receiving surface of the silicon substrate 1 in order to suppress the loss of reflection of incident sunlight, the surface orientation of the light receiving surface of the silicon substrate 1 is (100). Preferably there is.

  Next, as shown in FIG. 3, a p-type paste material 2 containing, for example, boron as a p-type impurity on the back surface opposite to the light-receiving surface of the silicon substrate 1, and an n-type paste material containing, for example, phosphorus as an n-type impurity. 3 is attached in a desired pattern shape, and the silicon substrate 1 is heated to a temperature of, for example, 100 ° C. to 200 ° C. in order to evaporate the organic solvent component contained in these paste materials. Is covered with a diffusion prevention film 4. Here, as means for attaching the paste material to a desired pattern shape, for example, screen printing or ink jet printing can be used. Further, as a pattern shape, in order to efficiently collect carriers generated in the silicon substrate 1, a p-type paste material 2 and an n-type paste material 3 are arranged along the back surface of the silicon substrate 1 as shown in FIG. Preferably, they are formed at alternately spaced intervals. The diffusion prevention film 4 is made of, for example, a silicon oxide film, and can be formed by forming a film by atmospheric pressure CVD or drying a coating solution containing silicon oxide.

  Subsequently, the silicon substrate 1 is put into a quartz furnace heated to, for example, 900 ° C. to 1000 ° C., and placed in the quartz furnace, for example, for 30 minutes to 60 minutes, whereby boron contained in the p-type paste material 2 is contained. Then, phosphorus contained in the n-type paste material 3 diffuses into the silicon substrate 1, and a plurality of p + layers 6 and n + layers 5 are alternately spaced along the back surface of the silicon substrate 1 as shown in FIG. Open and formed. Here, since the diffusion prevention film 4 is formed on the back surface of the silicon substrate 1, boron contained in the p-type paste material 2 and phosphorus contained in the n-type paste material 3 are diffused into the silicon substrate 1. Diffusion outside the silicon substrate 1 is prevented.

  Next, the silicon substrate 1 is immersed in a high-temperature aqueous solution containing, for example, an alkali such as sodium hydroxide or potassium hydroxide and isopropyl alcohol (IPA), and anisotropic etching along the silicon crystal orientation proceeds. As shown in FIG. 5, a fine pyramid-like texture structure 8 having a (111) plane is formed on the light receiving surface of the silicon substrate 1. Here, since the diffusion prevention film 4 is formed on the back surface of the silicon substrate 1, the back surface of the silicon substrate 1 is not etched.

  Next, as shown in FIG. 6, the silicon substrate 1 is immersed in hydrofluoric acid or the like, whereby the diffusion protective film 4, the p-type paste material 2, and the n-type paste material 3 on the back surface of the silicon substrate 1 are removed. . Then, as shown in FIG. 7, passivation films 9 and 10 for suppressing the surface recombination of carriers are formed on the light receiving surface and the back surface of the silicon substrate 1. As the passivation films 9 and 10, for example, a silicon oxide film formed by thermal oxidation or a silicon nitride film formed by a plasma CVD method can be used to effectively suppress the surface recombination of carriers. Here, when a silicon nitride film is used as the passivation film 9 formed on the light receiving surface of the silicon substrate 1, the refractive index thereof is about 2.1. Therefore, the silicon nitride film is the sun on the light receiving surface of the silicon substrate 1. It can also be used as an antireflection film that suppresses reflection of light.

  Next, in order to make electrical connection with the p + layer 6 and the n + layer 5 on the back surface of the silicon substrate 1, a passivation film 10 formed on the back surface of the silicon substrate 1 is desired as shown in FIG. Removed into pattern shape. Passivation film 10 is preferably removed in the form of dots or lines, for example, and the removal form is preferably determined according to the arrangement of p + layer 6 and n + layer 5. Further, the passivation film 10 inside the end portions of the p + layer 6 and the n + layer 5 is removed so that electrodes are not formed in portions other than the p + layer 6 and the n + layer 5. It is preferable.

  Finally, as shown in FIG. 9, the finger p electrode 11 is formed on the p + layer 6 and the finger n electrode 12 is formed on the n + layer 5 in accordance with the portion from which the passivation film 10 has been removed. The Here, as the electrode material of the finger p electrode 11 and the finger n electrode 12, a highly conductive material such as silver or aluminum may be used so that a current generated in the solar battery cell can be taken out sufficiently. preferable. Further, as means for forming the finger p electrode 11 and the finger n electrode 12, for example, means such as vapor deposition of an electrode material by electron beam heating in high vacuum, screen printing of a paste containing the electrode material, or plating of the electrode material is used. Can do. Furthermore, in order to obtain good ohmic contact between the silicon substrate 1 and the finger p-electrode 11 and the finger n-electrode 12, it is preferable that a heat treatment at 400 ° C. to 500 ° C. is performed after the electrode material is attached to the silicon substrate 1. In addition, the bus-bar electrode which cross | intersects a finger electrode is also formed with these finger electrodes.

The schematic plan view of FIG. 10 shows a preferable example of the electrode structure on the back surface of the solar battery cell of the present invention obtained as described above. As shown in FIG. 10, a plurality of finger p-electrodes 11 and finger n-electrodes 12 are linearly formed on the back surface of the solar cell so as to cover the entire back surface of the solar cell alternately. The bus bar n electrode 14 that intersects the n electrode 12 is formed inside the back surface, whereas the bus bar p electrode 13 that intersects the finger p electrode 11 is formed at the end of the back surface. By doing in this way, even if it is a case where the area of the back surface of a photovoltaic cell is the same by this invention and the conventional, the length L of the finger n electrode 12 and the finger p electrode 11 of the back surface of the photovoltaic cell of this invention ₁ is shorter than the length L _{0 of the} conventional finger n electrode 112 and finger p electrode 111 shown in FIG. Therefore, even when the area of the back surface of the solar battery cell is increased, the series resistance can be reduced, and not only the width W _{1 of} the finger n electrode 12 and the finger p electrode 11 but also the finger p electrode 11 and the finger n electrode 12. The pitch P ₁ between these can also be reduced. Therefore, in the present invention, even when the area of the back surface of the solar battery cell is increased, the carrier moving distance in the silicon substrate 1 is not increased, and the carrier collection efficiency in the finger electrode can be improved. Thus, a decrease in the output of the solar battery cell can be effectively suppressed.

The schematic plan view of FIG. 11 shows another preferred example of the electrode structure on the back surface of the solar battery cell of the present invention. As shown in FIG. 11, two bus bar n electrodes 14 intersecting the finger n electrode 12 and one bus bar p electrode 13 intersecting the finger p electrode 11 are formed inside the back surface of the solar battery cell. Yes. Therefore, even when the area of the back surface of the solar battery cell is increased, the length L ₁ of the finger n electrode 12 and the finger p electrode 11 can be shortened. Can be deterred.

10 and 11, the length L ₁ of the finger n electrode 12 and the finger p electrode 11 is preferably not more than ½ of the length L in the longitudinal direction of the finger electrode on the back surface of the solar battery cell. / 4 or less is more preferable, and 1/6 or less is more preferable. L ₁ is tend to not be able to effectively suppress a drop in output of the solar cell if it becomes large back surface area of the solar cell when greater than half of L, 1 L ₁ is L When it is / 4 or less, particularly 1/6 or less, even when the area of the back surface of the solar battery cell becomes large, a decrease in the output of the solar battery cell tends to be particularly effectively suppressed.

In the present specification, the length L ₁ of the finger electrode refers to the length from the contact point between the finger electrode and the bus bar electrode, as shown in FIGS. Further, when there are a plurality of finger electrodes, at least one of the finger electrodes may be in the above range, but it is preferable that all finger electrodes have a length in the above range.

  The schematic plan view of FIG. 12 shows a preferred example of the electrode structure on the back surface of the solar cell module of the present invention. As shown in FIG. 12, this solar cell module is a combination of four solar cells 50a, 50b, 50c, and 50d in which p + layers and n + layers are alternately formed on the back surface along the back surface. It is configured. Bus bar p-electrodes 13a, 13b, 13c, 13d and bus-bar n-electrodes 14a, 14b, 14c, 14d are respectively formed at both ends of the back surface of solar cells 50a, 50b, 50c, 50d. Bus bar electrodes are not formed inside the back surfaces of the cells 50a, 50b, 50c, 50d.

  However, the bus bar n electrodes 14a, 14b, 14c, and 14d of the solar cells 50a, 50b, 50c, and 50d are commonly used as one bus bar n electrode, so that the entire solar cell module has one bus bar n electrode. Is formed inside the back surface of the solar cell module, and as in the case of the above-described solar cell, even if the area of the back surface of the solar cell module becomes large, the reduction in output is effectively suppressed. Tend to be able to. Since the bus bar p-electrodes 13a, 13b, 13c, and 13d are separated and exist independently, the IV characteristics of the solar cells 50a, 50b, 50c, and 50d are evaluated and obtained from the evaluation. When there is a solar cell that is considered to have an adverse effect on the output of the entire solar cell module, the output of the entire solar cell module is reduced by not wiring the bus bar p electrode of the solar cell. Further, it can be effectively suppressed.

  In addition, in the said solar cell module, although the solar cell in which a bus-bar electrode was formed only in the edge part of a back surface was used, you may use the solar cell in which a bus-bar electrode is formed in the inside of a back surface. Needless to say, the preferred finger electrode length in the solar cell module is the same as that in the solar cell.

  Needless to say, in the solar battery cell and the solar battery module, the conductivity types of p and n may be interchanged.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

According to the present invention, it is possible to provide a method for manufacturing a solar cell that can effectively suppress a decrease in output even when the area of the back surface is increased. Therefore, the present invention provides a back junction solar cell. Or it can utilize suitably for manufacture of the solar cell module which combined several solar cell of the back junction type.

  1,101 Silicon substrate, 2 p-type paste material, 3 n-type paste material, 4 diffusion prevention film, 5,105 n + layer, 6,106 p + layer, 8 texture structure, 9,10 passivation film, 11,111 Finger p electrode, 12, 112 Finger n electrode, 13, 13a, 13b, 13c, 13d, 113 Bus bar p electrode, 14, 14a, 14b, 14c, 14d, 114 Bus bar n electrode, 50a, 50b, 50c, 50d Solar cell Cell, 109 Antireflection film.

Claims (2)

A method of manufacturing a solar battery cell in which a p + layer and an n + layer are formed on the back surface opposite to the light receiving surface of a semiconductor substrate,
Attaching a p-type paste material containing a p- type impurity and an n-type paste material containing an n-type impurity to the back surface of the semiconductor substrate;
Forming a diffusion barrier film on the back surface of the semiconductor substrate so as to cover the p-type paste material and the n-type paste material ;
Heating the semiconductor substrate to diffuse the p-type impurities contained in the p-type paste material into the semiconductor substrate to form a p + layer;
Heating the semiconductor substrate to diffuse the n-type impurities contained in the n-type paste material into the semiconductor substrate to form an n + layer;
Forming a texture structure by etching the light receiving surface of the semiconductor substrate,
In the step of forming the texture structure, the diffusion prevention film also serves as an etching mask when the texture structure is formed . The method for manufacturing a solar cell according to claim 1, wherein the diffusion prevention film is made of a silicon oxide film.

Images